Although several OTC ovulation texts exist, none are suitable for contraception applications because they detect luteinizing hormone (LH) which exhibits a peak preceding ovulation by only 16-36 hours. This research would develop a fertile period prediction system based upon the presence of an increase in urinary estrone-3-glucuronide (E1-g) 72 hours prior to ovulation and an increase in pregnanediol glucuronide (Pd-g) following ovulation. The mean value of E1-g rises by a factor of three two days prior to the LH peak, but its more gradual rise requires a more quantitative detection device than the on or off color OTC LH tests. This obstacle would be overcome by employing a novel, competitive, immunoassay- based, total internal reflectance fluorescence (TIRF) biosensor consisting of a quartz fiber probe which had been pretreated with covalently bound E1-g and previously incubated with antibody to E1-g bearing fluorescent molecules. As urinary E1-g competed with the bound E1-g, the antibody would migrate into the urine sample thus reducing the fluorescent signal. When the sensor measures the E1-g increase prior to ovulation, its control unit would signal the beginning of a fertile period. A similar sensor for pregnanediol glucuronide would signal the end of the fertile period.